1. Field of the Invention
The present invention relates to a projection display device for projecting light modulated by an imager onto a projection plane.
2. Description of the Related Art
A projection display device (hereinafter, called as a “projector”) is constructed in such a manner that light from a light source is modulated by a light modulator constituted of an imager (such as a liquid crystal panel) to project the modulated light (hereinafter called as “image light”) onto a projection plane. Polarizers are disposed on an incident side and an exit side of the light modulator. A large amount of heat is generated from the light modulator and the polarizers when light is passed through the light modulator and the polarizers. In particular, a largest amount of heat is generated from the polarizer on the exit side of the light modulator.
In view of the above, a conventional projector is designed to cool the light modulator and the polarizers by cooling air.
FIG. 9 is a diagram showing an example of a cooling structure for a light modulator and polarizers.
Two output-side polarizers 2 are disposed on the exit side of a light modulator 1. A dichroic prism 3 is disposed on the exit side of the output-side polarizers 2. A support member 4 is mounted on a surface of the light modulator 1 at a position facing the output-side polarizers 2.
An air outlet port 5 is formed at a position below the light modulator 1 and the output-side polarizers 2. Cooling air generated by an unillustrated fan is blown through the air outlet port 5. The cooling air is mainly allowed to flow in a space between the light modulator 1 and the output-side polarizers 2. Therefore, the light modulator 1 and the output-side polarizers 2 are cooled.
Although not illustrated, another two sets of a light modulator 1 and output-side polarizers 2 are disposed on the other two surfaces of the dichroic prism 3 respectively to modulate light of a red wavelength band, light of a green wavelength band, and light of a blue wavelength band. In this example, only the cooling structure for one set of the light modulator 1 and the output-side polarizers 2 is shown. However, the cooling structures for the other two sets of the light modulator 1 and the output-side polarizers 2 are substantially the same as the cooling structure for the one set.
As shown in FIG. 9, the light modulator 1 includes an imager (liquid crystal panel) 1a, and a frame 1b surrounding the perimeter of the imager 1a. It is often the case that the lateral thickness of the frame 1b is set larger than the thickness of the imager 1a. In this case, a step portion S is formed between the imager 1a and the frame 1b on the exit side of the light modulator 1.
In the above arrangement, when cooling air (indicated by the black arrows in FIG. 9) is allowed to flow in a space between the light modulator 1 and the output-side polarizers 2, air turbulence (indicated by the white arrow in FIG. 9) is generated around the step portion S. As a result, dirt or dust contained in the cooling air may stagnate on the step portion S, and smear a periphery of the imager 1a. Therefore, an illuminance of image light which has been passed through the smeared periphery of the imager 1a may be lowered, or discoloration may appear.
In recent years, as the light amount of a light source has been increased due to high luminance of image light, the amount of heat generated on or around the light modulator 1 has been increasing. In view of this, it is necessary to increase the flow rate of cooling air, which may likely to cause deterioration of a projected image due to adhesion of dust or a like matter.